1. Field of the Invention
The present invention relates to an apparatus for guiding conveyance of a sheet of paper in a duplex printer, which guides and reverses the paper in the duplex printer for duplex printing, and more particularly, to a paper conveyance guiding apparatus having a shortened paper reverse passage and a reversible rotation roller in a duplex printer.
2. Description of the Related Art
Generally, a printing apparatus, such as a printer or a photocopying machine, feeds a sheet of paper, prints a desired image on a first side of the paper, and discharges the printed paper to an outside of the printing apparatus. Therefore, as the image is printed on only the first side of the paper when the paper is fed once, a user has to manually reverse the paper having the printed first side to print another image on a second side of the paper. To avoid the above troubles, a duplex printer, which prints the images on respective ones of both first and second sides of the paper with one time feed and discharges the printed paper, has been introduced. FIG. 1 is a view showing one example of the duplex printer.
As shown in FIG. 1, the duplex printer has a paper conveyance guiding apparatus disposed at a printing unit 10 to perform a printing job in order to reverse a sheet of paper having the first side and the second side and pass therethrough.
Referring to FIG. 1, the paper conveyance guiding apparatus of the general duplex printer has an entrance passage 20 disposed on a way to the printing unit 10 in order to allow the paper to enter the printing unit 10, a discharge passage 30 disposed on a way out of the printing unit 10 in order to guide and discharge the printed paper to an outside of a printing body 1, a reverse passage 40 branched off from the discharge passage 30 to reverse the paper to the way to the printing unit 10, and an intermediate passage 50 to connect the reverse passage 40 and the entrance passage 20.
The printing unit 10 includes a paper conveying passage 11, a developing unit 12 disposed in a regular interval on the paper conveying passage 11, and a settlement unit 13.
The entrance passage 20 has a feed roller 21 and a register roller 22 to convey the paper entered into the entrance passage 20 after being picked up by a pick-up roller 3 from a feed cassette 2. In addition, a first discharging roller 14 is disposed at the way out of the printing unit 10 in order to convey the printed paper in a discharging direction, and a discharging sensor 15 disposed near the first discharging roller 14 to sense the paper passing through the printing unit 10. The discharging sensor 15 sends a sensing signal of sensing the paper passing through the printing unit 10 to a controller (not shown). Furthermore, a second discharging roller 31 and a third discharging roller 32 are disposed at the discharge passage 30. In FIG. 1, reference numerals 33, 34 and 35 are idle rollers.
The reverse passage 40 is partitioned from the discharge passage 30 using a paper guide 41, and a reverse roller 42 is disposed on a way from the reverse passage 40 to the intermediate passage 50 in order to push the reversed paper into the intermediate passage 50.
The intermediate passage 50 is formed to be connected with the entrance passage 20 by passing a lower side of the printing body 1 from the way out of the reverse roller 42, and a plurality of conveying rollers 51 are disposed on the intermediate passage 50.
An operation of the conventional paper conveyance guiding apparatus having above structure as follows.
As shown in FIG. 1, the image is printed on the first side of the paper as the paper enters to the printing unit 10 through the entrance passage 20 and is conveyed to the paper conveyance passage 11. As shown in FIGS. 2 and 3, the paper is continuously conveyed along the discharge passage 30 by the first discharging roller 14, which is disposed on the way out of the printing unit 10, and the second discharging roller 31 and the third discharging roller 32 disposed in the discharge passage 30. At this time, the discharging sensor 15 detects a rear end of the paper passing through the settlement unit 13 and entering the discharging passage 30. Here, when the user selects simplex printing to print on the first side of the paper, the paper is discharged to a discharging tray 4 by the third discharging roller 32.
When duplex printing is selected as shown in FIG. 4, the third discharging roller 32 is driven in a reverse direction by a control signal of the controller simultaneously when the rear end of the paper is come out from the paper guide 41, thus the paper is no longer conveyed in the discharging direction. Then, the paper passes through the reverse passage 40 to be engaged with the reverse roller 42 in a state that the first and second sides of the paper are reversed. Accordingly, the paper reenters the printing unit 10 through the intermediate passage 50 and the entrance passage 20 in the state that the first and second sides of the paper are reversed, and the printing is operated on the second side of the paper. The printed paper is discharged to the discharging tray 4 through the discharge passage 30.
However, according to the paper conveyance guiding apparatus of the conventional duplex printer described so far, there should be the separate reverse passage 40 to reverse the paper and the separate reverse roller 42 to allow the reversed paper to enter the intermediate passage 50 and convey the paper to the printing unit 10, thus a structure of the duplex printer is complicated and a production cost is increased as there are a lot of elements required in the duplex printer.
In addition, as a space for installation of the paper guide 41 and the reverse roller 42 to form the separate reverse passage 40 should be secured, it cannot be avoided that an external appearance becomes massive.
Furthermore, the paper conveyance guiding apparatus of the conventional duplex printer has the paper conveying passage 11 to convey the paper through the reverse passage 40 after an end portion of the paper comes out from the paper guide 41 by discharging the paper to the third discharging roller 32 when the paper is reversed for the duplex printing, thus the paper conveying passage becomes longer, and an efficiency of the duplex printing deteriorates.